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<h4 class="subsection" id="SH-Function-Attributes-1"><span>6.33.29 SH Function Attributes<a class="copiable-link" href="#SH-Function-Attributes-1"> &para;</a></span></h4>

<p>These function attributes are supported on the SH family of processors:
</p>
<dl class="table">
<dt><a class="index-entry-id" id="index-calling-functions-through-the-function-vector-on-SH2A"></a>
<a id="index-function_005fvector-function-attribute_002c-SH"></a><span><code class="code">function_vector</code><a class="copiable-link" href="#index-function_005fvector-function-attribute_002c-SH"> &para;</a></span></dt>
<dd><p>On SH2A targets, this attribute declares a function to be called using the
TBR relative addressing mode.  The argument to this attribute is the entry
number of the same function in a vector table containing all the TBR
relative addressable functions.  For correct operation the TBR must be setup
accordingly to point to the start of the vector table before any functions with
this attribute are invoked.  Usually a good place to do the initialization is
the startup routine.  The TBR relative vector table can have at max 256 function
entries.  The jumps to these functions are generated using a SH2A specific,
non delayed branch instruction JSR/N @(disp8,TBR).  You must use GAS and GLD
from GNU binutils version 2.7 or later for this attribute to work correctly.
</p>
<p>In an application, for a function being called once, this attribute
saves at least 8 bytes of code; and if other successive calls are being
made to the same function, it saves 2 bytes of code per each of these
calls.
</p>
</dd>
<dt><a id="index-interrupt_005fhandler-function-attribute_002c-SH"></a><span><code class="code">interrupt_handler</code><a class="copiable-link" href="#index-interrupt_005fhandler-function-attribute_002c-SH"> &para;</a></span></dt>
<dd><p>Use this attribute to
indicate that the specified function is an interrupt handler.  The compiler
generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
</p>
</dd>
<dt><a id="index-nosave_005flow_005fregs-function-attribute_002c-SH"></a><span><code class="code">nosave_low_regs</code><a class="copiable-link" href="#index-nosave_005flow_005fregs-function-attribute_002c-SH"> &para;</a></span></dt>
<dd><p>Use this attribute on SH targets to indicate that an <code class="code">interrupt_handler</code>
function should not save and restore registers R0..R7.  This can be used on SH3*
and SH4* targets that have a second R0..R7 register bank for non-reentrant
interrupt handlers.
</p>
</dd>
<dt><a id="index-renesas-function-attribute_002c-SH"></a><span><code class="code">renesas</code><a class="copiable-link" href="#index-renesas-function-attribute_002c-SH"> &para;</a></span></dt>
<dd><p>On SH targets this attribute specifies that the function or struct follows the
Renesas ABI.
</p>
</dd>
<dt><a id="index-resbank-function-attribute_002c-SH"></a><span><code class="code">resbank</code><a class="copiable-link" href="#index-resbank-function-attribute_002c-SH"> &para;</a></span></dt>
<dd><p>On the SH2A target, this attribute enables the high-speed register
saving and restoration using a register bank for <code class="code">interrupt_handler</code>
routines.  Saving to the bank is performed automatically after the CPU
accepts an interrupt that uses a register bank.
</p>
<p>The nineteen 32-bit registers comprising general register R0 to R14,
control register GBR, and system registers MACH, MACL, and PR and the
vector table address offset are saved into a register bank.  Register
banks are stacked in first-in last-out (FILO) sequence.  Restoration
from the bank is executed by issuing a RESBANK instruction.
</p>
</dd>
<dt><a id="index-sp_005fswitch-function-attribute_002c-SH"></a><span><code class="code">sp_switch</code><a class="copiable-link" href="#index-sp_005fswitch-function-attribute_002c-SH"> &para;</a></span></dt>
<dd><p>Use this attribute on the SH to indicate an <code class="code">interrupt_handler</code>
function should switch to an alternate stack.  It expects a string
argument that names a global variable holding the address of the
alternate stack.
</p>
<div class="example smallexample">
<pre class="example-preformatted">void *alt_stack;
void f () __attribute__ ((interrupt_handler,
                          sp_switch (&quot;alt_stack&quot;)));
</pre></div>

</dd>
<dt><a id="index-trap_005fexit-function-attribute_002c-SH"></a><span><code class="code">trap_exit</code><a class="copiable-link" href="#index-trap_005fexit-function-attribute_002c-SH"> &para;</a></span></dt>
<dd><p>Use this attribute on the SH for an <code class="code">interrupt_handler</code> to return using
<code class="code">trapa</code> instead of <code class="code">rte</code>.  This attribute expects an integer
argument specifying the trap number to be used.
</p>
</dd>
<dt><a id="index-trapa_005fhandler-function-attribute_002c-SH"></a><span><code class="code">trapa_handler</code><a class="copiable-link" href="#index-trapa_005fhandler-function-attribute_002c-SH"> &para;</a></span></dt>
<dd><p>On SH targets this function attribute is similar to <code class="code">interrupt_handler</code>
but it does not save and restore all registers.
</p></dd>
</dl>

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